Recently, an ultrasound system has been extensively used in the medical field due to its non-invasive and non-destructive nature. Modern high-performance ultrasound imaging diagnostic systems and techniques are commonly used to produce two- or three-dimensional ultrasound images of internal features of patients. In order to provide the ultrasound images, the ultrasound system operates in various image modes such as a brightness mode, a Doppler mode and the like to acquire ultrasound images for diagnosis.
In the Doppler mode, the ultrasound system provides a color flow image showing velocities of moving objects such as blood flow, a heart, etc. The color flow image may be formed based on Doppler signals obtained by alternately transmitting and receiving ultrasound signals to and from a target object. The Doppler signals may contain low frequency signals due to the motion of cardiac walls or valves of a heart. The low frequency signals (so-called clutter signals) have amplitude of over 100 times than that of normal Doppler signals obtained from the blood flow. The clutter signals may be an obstacle to accurately detect velocities of the blood flow. Thus, it is required to remove the clutter signals from the Doppler signals for accurate detection. The ultrasound system adopts clutter filters, which are types of a high pass filter, to remove the clutter signals.
The clutter filters of a conventional ultrasound system remove the clutter signals with a specific cutoff frequency. In such a case, if the cutoff frequency is highly set, then the Doppler signals of a relatively low frequency may be also cut off with the clutter signals. Thus, it may be difficult to accurately detect the velocities of the blood flow.